Rendering a 3-D scene using secondary ray tracing

ABSTRACT

During tracing of a primary ray in a 3-D space (e.g., a 3-D scene in graphics rendering), a ray is found to intersect a primitive (e.g., a triangle) located in the 3-D space. Secondary ray(s) may be generated for a variety of purposes. For example, occlusion rays may be generated to test occlusion of a point of intersection between the primary ray and primitive is illuminated by any of the light(s). An origin for each secondary ray can be modified from the intersection point based on characteristics of the primitive intersected. For example, an offset from the intersection point can be calculated using barycentric coordinates of the intersection point and interpolation of one or more parameters associated with vertices defining the primitive. These parameters may include a size of the primitive and differences between a geometric normal for the primitive and a respective additional vector supplied with each vertex.

BACKGROUND Field

The present invention generally relates to ray tracing based renderingtwo-dimension representations from three-dimensional scenes, and in oneparticular aspect, to tracing of secondary rays in ray tracing forrendering of images from 3-D scenes.

Description of Related Art

Rendering photo-realistic images with ray tracing is known to producephoto-realistic images, including realistic shadow and lighting effects,because ray tracing can model the physical behavior of light interactingwith elements of a scene. Ray tracing usually involves obtaining a scenedescription composed of geometric primitives, such as triangles, thatdescribe surfaces of structures in the scene, and modeling how lightinteracts with primitives in the scene by tracing light rays, startingfrom a virtual camera, through numerous potential interactions withscene objects, until terminating either at light sources, or exiting thescene without intersecting a light source. Additionally, when a surfaceis found to have been intersected by a ray, additional rays may be usedto determine whether that intersected surface is in shadow frompotential sources of light energy, and for other purposes, such as forcharacterizing reflections or refractions.

SUMMARY

Generating images using ray tracing can be computationally expensive,with computation required for two principal categories of activities:testing rays for intersection and shading identified ray intersections.Different surfaces require different intersection testing algorithms,and in some cases a variety of algorithms exist to test a particularkind of surface. In general, simpler surfaces can be tested forintersection using algorithms that require less computational cost. Forexample, testing a planar primitive, such as a triangle, is easier thantesting a higher-order surface. However, a mesh of polygons (e.g., atriangle mesh) is only an approximation of an original surface, andwhere relatively-low polygon count models are used, there may berelatively significant deviation from the polygon mesh and the originalmodel.

One area of ray tracing rendering affected thereby is the determinationof the casting of secondary rays from an intersection identified for aprimary ray. For example, when a primary ray is found to haveintersected a surface, occlusion rays may be cast to determine shadowingat the point of intersection. For example, rays may be cast towardslights in the scene. Casting rays that originate from surfaces of planarpolygon surfaces can result in hard and unrealistic shadowing effects.However, increasing polygon counts for scene objects is undesirable, inthat more memory to store subject objects will be required. Implementingray tracing rendering by testing higher order surfaces for intersectionalso poses challenges.

In one aspect, a method of tracing secondary rays, such as occlusionrays, from an intersection point is introduced. In such method, one ormore secondary rays are defined to have respective origins that areoffset from the surface. In one example, an offset is determinedaccording to vectors associated with vertices defining the intersectedsurface. In one example, an implicit higher order surface can be modeledby varying an amount of offsets for rays found to intersect the surfaceat different points. A direction of offset can be along a normaldirection of the surface, or along a direction of the ray that was foundto intersect the surface, and resulting in such occlusion ray(s). Forexample, where a number of parent rays intersect the same primitive atdifferent locations, and secondary ray(s) are to be traced for each ray,those secondary rays are defined to have an origin offset from thesurface of the primitive in varying amounts. An amount of offset isvariable among the secondary rays and dependent on an intersectionlocation of a respective parent ray on the primitive.

In another aspect, an apparatus for ray tracing a 3-D scene comprises aray intersector configured for identifying an intersection point betweena primary ray and a primitive defining a surface located in the 3-Dscene. The apparatus also comprises a specifier of a secondary rayconfigured for specifying a secondary ray to be emitted for tracing inthe 3-D scene, the secondary ray having an origin and a direction. Thespecifier is configured to determine a position of the origin of thesecondary ray by determining an offset amount from the intersectionpoint. The offset amount is dependent on a relative position of theintersection point to vertices defining the surface located in the 3-Dscene. The specifier is coupled to the ray intersector for providing thesecondary ray to be tested for intersection by the ray intersector. Thespecifier can be coupled to the ray intersector through a call providedby an Application Programming Interface. The ray intersector can beimplemented by instructions configuring a processor to execute anintersection testing algorithm. The ray intersector can be implementedwith fixed function and/or limited programmability elements that canexecute specific portions of an intersection testing algorithm (e.g.,traversing a ray through an acceleration structure and testing a ray forintersection with a primitive). The specifier may comprise a portion ofshader code configuring a processor, in response based on anintersection between the primary ray and the primitive.

Another aspect includes a non-transitory machine readable medium havingstored thereon machine readable data and instructions. The data andinstructions comprise instructions for reading data defining meshes ofplanar primitives located in the 3-D scene. Each primitive is defined bya set of vertexes located in respective positions in the 3-D scene, andhaving associated therewith respective vectors. The instructions alsocomprise instructions for generating a set of offset coefficients fromthe positions of the vertices in the 3-D scene and the vectorsassociated with the vertices and for tracing a primary ray in the 3-Dscene to identify an intersection point between the primary ray and aprimitive. The instructions also comprise instructions for determining asecondary ray in response to identifying the intersection point of theprimary ray. The secondary ray has an origin offset from theintersection point of the primary ray by an amount determined based onthe offset coefficients and a relative position of the intersectionpoint on the primitive.

The functional aspects described can be implemented as modules, such asmodules of computer executable code, configuring appropriate hardwareresources operable to produce inputs and outputs as described.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of aspects and examples disclosed herein,reference is made to the accompanying drawings in the followingdescription.

FIG. 1 depicts a planar primitive (e.g., a triangle) defined by verticesand associated with data used in an example implementation of thedisclosure;

FIG. 2 depicts a situation where a primary ray is found to intersect aprimitive, and secondary rays, such as occlusion rays are defined, to betraced in the 3-D scene;

FIG. 3 depicts a side-view of a primitive and an example approach todefining secondary rays with origin offsets according to the disclosure;

FIG. 4 depicts a side-view of a further example of secondary rays havingorigin offsets according to the disclosure;

FIG. 5 depicts an aspect of clamping a calculated origin offset underspecified conditions;

FIG. 6 depicts an example process of pre-processing data to be used inimplementing embodiments of the disclosure;

FIG. 7 depicts an example approach to generating data that can be usedto implement an example according to the disclosure;

FIG. 8 depicts an example process of ray tracing;

FIG. 9 depicts an example process that can be used in the processdepicted in FIG. 8, to implement origin offsets according to thedisclosure;

FIG. 10 depicts an example apparatus in which disclosed aspects ofsecondary ray origin offsetting can be practiced; and

FIG. 11 depicts another example apparatus in which disclosed aspects ofsecondary ray origin offsetting can be practiced.

DETAILED DESCRIPTION

The following description is presented to enable a person of ordinaryskill in the art to make and use various aspects of the inventions.Descriptions of specific techniques, implementations and applicationsare provided only as examples. Various modifications to the examplesdescribed herein may be apparent to those skilled in the art, and thegeneral principles defined herein may be applied to other examples andapplications without departing from the scope of the invention.

As introduced in the background, a 3-D scene needs to be converted intoa 2-D representation for display. Such conversion may include selectinga camera position, from which the scene is viewed. The camera positionfrequently represents a location of a viewer of the scene (e.g., agamer, a person watching an animated film, etc.) The 2-D representationis usually at a plane location between the camera and the scene, suchthat the 2-D representation comprises an array of pixels at a desiredresolution. A color vector for each pixel is determined throughrendering. During ray tracing, rays can be initially cast from thecamera position and intersect the plane of the 2-D representation atdifferent points, and continue in(to) the 3-D scene.

For clarity in description, data for a certain type of object, e.g., aprimitive (e.g., coordinates for three vertices of a triangle) often isdescribed simply as the object itself, rather than referring to the datafor the object. For example, if referring to “fetching a primitive”, itis to be understood that data representative of that primitive is beingfetched.

Representing realistic and finely detailed objects in the 3-D scene isusually done by providing a large number of planar geometric primitivesthat approximate a surface of the object (i.e., a wire frame model). Assuch, a more intricate object may need to be represented with moreprimitives and smaller primitives than a simpler object. Althoughproviding a benefit of higher resolution, performing intersection testsbetween rays and larger numbers of primitives (as described above, andas will be described further below) is computationally intensive,especially since a complex scene may have many objects. Also, storagerequirements increase as the number of primitives used to represent anobject increases.

FIG. 1 depicts a planar primitive 2 being defined using three vertexes5-7. In addition to position information for the vertexes, the primitivecan be defined using a per-primitive normal 11 that defines an outerface of the primitive. FIG. 1 depicts a conceptual example of how aprimitive may be defined by data stored on a non-transitory medium. Inpractice, primitive 2 can be defined within a mesh of primitives, wherea set of vertices has connectivity information associated with it, forexample. Thus, FIG. 1 does not explicitly or implicitly limit or requireany particular approach to defining a planar primitive. Also, FIG. 1depicts an example of a triangular planar primitive, but implementationsof the disclosure can be used with other kinds of planar primitives.Still further implementations may be able to test non-planar primitivesfor intersection, and implement origin offsetting from intersectionpoints according to the disclosure for such non-planar surface as well.However, a need for implementing such offsetting is generally expectedto be less, in that a non-planar surface may be defined to more closelyrepresent an idealized surface.

FIG. 2 depicts a situation where a primary ray 15 is found to intersectprimitive 2 at an intersection point 20. Finding an intersection betweenprimary ray 15 and primitive 2 is performed using an intersection testalgorithm that uses the planar primitive. Primary ray 15 can be any raybeing traced in the system, and is “primary” relative to “secondary”rays that may be generated in response to finding an intersection forthat ray. For example, a primary ray may itself be a secondary ray ofanother ray. A variety of algorithms to perform such intersectiontesting exist. In one implementation, a by-product of the intersectiontesting producing barycentric coordinates for intersection point 20.FIG. 2 also depicts that secondary rays are generated in response tofinding intersection point 20 for primary ray 15. The example secondaryrays of FIG. 2 include occlusion rays 31 and 32 respectively directedtowards light sources 26 and 25. In one example, light sources 25 and 26can be identified point or area sources of light energy entering thescene. For example, light sources 25 and 26 can be enumerated inposition and have known characteristics. An ambient occlusion ray 32also is shown being emitted from intersection point 20. Such ambientocclusion ray 32 may be part of a set of ambient occlusion rays that arestochastically generated. Examples of other kinds of secondary raysinclude reflection and refraction rays that would be emitted from theorigin in a direction influenced by characteristics of a material ofprimitive 2. This disclosure concerning secondary rays is by way ofexample and not limitation as to the kinds of rays to which the originoffsetting can be applied. Rays also can be represented using a varietyof formats, such as using an origin and direction, a line segmentdefined by two end points, a 5-D representation, and so on. As such, nolimitation is explicit or implied as to how such rays may berepresented.

FIG. 3 depicts a side view of primitive 2, showing a line defined byvertex 5 and vertex 7 (see FIG. 1), and depicts a variety of elementsused to illustrate an example according to the disclosure. Artistvectors 12 and 13 are respectively associated with vertexes 5 and 7. Aplane 39 perpendicular to artist vector 12, and a plane 38 perpendicularto artist vector 13 are shown in cross section. FIG. 3 depicts that animplicit curved surface 40 is defined to be tangent to plane 38 atvertex 7 and to plane 39 at vertex 5. Thus, artist vectors 12 and 13control a relative orientation of implicit curved surface 40 to theplanar surface of primitive 2. For example, a more obtuse angle definedby artist vectors 12 and 13 and the surface of primitive 2, would resultin a larger angle of departure of implicit surface 40 from the surfaceof primitive 2. In one example, implicit surface 40 is implicit in thesense that a point on implicit surface 40 can be determined for a givenlocation on primitive 2 and using that location as input to a proceduraldefinition or a parametric definition of implicit surface 40. In oneexample, implicit surface 40 is defined using a set of offsetcoefficients determined from the artist vector for each of the verticesand a polynomial (e.g., cubic) function that blends these offsetcoefficients using barycentric coordinates for an intersection point,for which an offset is to be determined. Extrapolating from this 2-Dexample, it would be understood that implicit surface 40 also would betangent to a plane perpendicular to an artist vector for the thirdvertex (for a triangle), not depicted in FIG. 3. Also, although implicitsurface 40 is shown to intersect each of vertices 5 and 7, there is norequirement that an implicit surface used to implement these disclosureshave such a characteristic. For example, implicit surface 40 can stillbe tangent to planes 38 and 39 at another location, such as a positionor offset along vectors 12 and 13.

In FIG. 3, ray 15 is shown hitting primitive 2 at intersection point 20,and that an original occlusion ray 31, which has an origin atintersection point 20, would be cast towards light 26. However, in FIG.3, instead of casting occlusion ray 31, an offset is determined, and anocclusion ray is cast from an offset origin 42, which is located basedon the offset (which in this conceptual depiction, locates the offsetorigin to a position on implicit surface 40). For example, modifiedocclusion ray 36 represents a ray cast from offset origin 42, determinedby offsetting along per-primitive normal 11 a calculated amount.Alternatively or additionally, a ray can be cast from an origin along adirection of ray 15. In the depiction of FIG. 3, an intersection pointbetween implicit surface 40 and ray 15 can be used to locate offsetorigin 41 (an origin for modified occlusion ray 35.) By definition, theintersection point between ray 15 and implicit surface 40 is an offsetamount along ray 15, calculated according to the definition used forimplicit surface 40.

A person of ordinary skill may understand from FIG. 3 that embodimentsof the disclosure may have a characteristic that a geometric model mayinclude or be associated with data that is interpretable to control anamount and a distribution of possible offset that for secondary rays tobe cast in response to intersections with primitive 2. Additionally, asize of primitive 2 also controls how large the amount of possibleoffset can be, where a larger primitive may have a larger offset, ingeneral. A direction along which a calculated offset amount can beapplied may be along an original incoming ray direction, or along ageometric normal, for example. In still further implementations, originsmay be offset in a random or pseudorandom direction from an intersectionpoint.

FIG. 4 depicts another example of how offsets can be determined and mayvary with an intersection point on the surface of a primitive. FIG. 4depicts vertexes 51 and 52, each associated with a respective artistvector 53 and 54, used in defining a primitive 50. Applying thedisclosure above concerning construction of implicit surface 40 to theparticulars of FIG. 4 results in a surface, that has a cross sectionlike that of implicit surface 55. Implicit surface 55 thus isnon-symmetrical, in that artist vectors 53 and 54 also are notsymmetrical. Since artist vector 54 produces a less obtuse anglerelative to primitive 50 than artist vector 53, implicit surface 55deviates less from primitive 50 near vertex 52 than near vertex 51. Ingeneral, implicit surfaces 40 and 55 can be viewed as a domain of afunction over the range of inputs that define a valid intersection pointin primitives 2 and 50, respectively. Examples of such mapping fordifferent intersection points is shown in FIG. 4 by points 60, 61 and 62on primitive 50 that respectively map to points 63, 64 and 65 onimplicit surface 55.

FIG. 5 exemplifies a further situation to be accounted for in someimplementations. In FIG. 5, a primitive 70 is defined from vertices 71and 72 (other vertices defining primitive 70 not depicted). Artistvectors 76 and 75 make acute angles with primitive 70, by contrast withboth FIG. 3 and FIG. 4, in which artist vectors made obtuse angles withrespect to their primitives. As such, if an implicit surface isdetermined in accordance with the examples above, then such surfacewould be “under” the surface of primitive 70, as shown by implicitsurface 73. Here, “under” is relative to a direction of per-primitivenormal 82, which points in a “front facing” direction. Locating anorigin for a secondary ray on a side opposite from a direction in whichnormal 82 was pointing from would result in erroneous behavior, ingeneral. Thus, in such a circumstance, an offset can be clipped so thatthe origin remains either on a surface of primitive 70, or anotherdefined minimum offset that does not put the origin for a secondary rayon the “back side” of primitive 70.

The depiction of implicit surface 40 is for assisting in conceptualizingan implementation according to the disclosure, but such implementationsdo not need to have defined such a surface, but rather may implement amechanism to provide an initial measure of potential offset, whichrelates to characteristics of the geometric model of which the primitiveis a part. This initial measure of potential offset can be modifiedbased on a specific intersection point on the primitive to arrive at afinal offset value, or a final position for an origin of a secondaryray.

A more specific example implementation of the disclosures in FIGS. 1-5is disclosed with respect to FIGS. 6-10 and in the appendix attachedhereto, which includes an example set of machine executable instructionsfor configuring a machine to perform an implementation of thedisclosure.

FIG. 6 depicts an example process that can be performed in animplementation according to the disclosure. FIG. 6 depicts that such aprocess may comprise, at 205, specifying a model for origin shifting ofsecondary rays (e.g., occlusion rays). Specifying a model may includedetermining a convention for defining a function that maps intersectionpoints on a surface of a primitive to respective points offset from thesurface of the primitive. In some implementations, a portion of thecalculations to be performed in determining such intersection-specificoffsets can be invariant to the intersection point, and can be performedin advance. At 207, such calculations are performed and at 209, dataresulting from these calculations is stored in association with theprimitive. Here, being stored in association provides that such data canbe retrieved when needed to determine an offset for a particularintersection point, or for other purposes, but does not require anyparticular organization or relative arrangement of data defining theprimitive and the pre-computed data. An example of computation that maybe performed pursuant to 207 is depicted in FIG. 7.

In FIG. 7, at 211, Dot Products (DPs) between an artist vectorassociated with each vertex and a vector determined from an origin of a3-D scene to the location of each vertex defining the primitive istaken. For example, considering vertex 5 of primitive 2, dot productsbetween artist vector 12, and each of the three vectors from a sceneorigin (in which primitive 2 is located) to vertexes 5, 6 and 7 arecalculated. This set of dot products is calculated for each of thevertexes, so that nine dot products would be calculated for primitive 2at process portion 211 of FIG. 7.

At 213, a reciprocal of a dot product between each artist vector and thegeometric normal for the primitive is taken. For primitive 2, this wouldinvolve performing three dot product operations and then taking areciprocal for each.

At 215, for each vertex, differences between the DP of the artist vectorfor this vertex and the origin/position vector for this vertex(calculated at 211) and each DP between the artist vector for thisvertex and the origin/position vectors for the other vertexes are taken.For example, considering vertex 5 of primitive 2 in FIG. 1, a DP (“firstDP”) was taken between artist vector 12 and a vector defined between theorigin of the 3-D scene and the position of vertex 5. Also, a respectiveDP was taken between artist vector 12 and vectors between the 3-D sceneorigin and the positions for each of vertexes 6 and 7 (“second DP” and“third DP”, respectively). At 215, the first DP is differenced withrespect to each of the second DP and the third DP. Each of vertexes 6and 7 are treated similarly. This gives a set of two offset coefficientsfor each vertex, in the direction of each of the other two vertices ofprimitive 2. The calculations described here are an implementation toproduce offset coefficients having a magnitude related to the size ofprimitive 2; as such, this example can be adapted or used to informthose of ordinary skill to implement other approaches to producepre-computed data having this characteristic. At 217, the offsetcoefficients are multiplied by the respective reciprocal calculated at213 (e.g., the pair of coefficients for vertex 5 are multiplied by thereciprocal involving artist vector 12). The resulting 3 pairs ofcoefficients can then be stored in association or for later use indetermining offsets for specific intersection points on primitive 2.

FIG. 8 depicts an example process of ray tracing, in which can beincorporated the origin offsetting disclosures found herein. At 223, anintersection between a primary ray and a primitive is identified. At224, a respective direction for each secondary ray is determined and at225, secondary ray(s) are defined to have origins that are offset froman intersection point of the primary ray and the primitive by an offsetamount, determined by applying an offset determination procedure (anexample of which is disclosed in more detail in FIG. 9). At 227, thesecondary ray(s) are traced. At 229, shading characteristics for theprimitive surface are determined using results of tracing the secondaryray(s) (as would be understood, such process can be iterative andrepetitive, such that this example does not imply that shading resultsare computed directly from any specific secondary ray, but that thesetraced secondary rays may contribute in some way to a shadingcharacteristic of the primitive surface).

FIG. 9 depicts a more specific example of how an offset for a particularintersection point can be determined, relying on the previousdisclosures herein. At 240, offset coefficients for each vertex arecomputed or accessed. These offset coefficients can be computed by animplementation according to the example of FIG. 7, or accessed, if thesecoefficients were generated in advance. At 242, the offset coefficientsmay be clamped to a minimum value, in dependence on a direction of thesecondary ray and the per-primitive normal. Such clamping, if applied,is to avoid a situation where an offset would otherwise put the originon an “inside” of the primitive (i.e., opposite to a direction of theper-primitive normal). At 244, barycentric coordinates of a particularintersection point are accessed, if produced as a byproduct ofintersection testing, or calculated. At 246, the barycentric coordinatesare used in a weighted blending of the offset coefficients to produce anoffset value to be applied to one or more secondary rays to be cast forthat intersection. See the Appendix for a more specific example ofmachine usable code that can be used to implement aspects of thedisclosure.

The above exemplary processes and portions thereof showed one way toimplement an example approach to offsetting origins of secondary rays,where an amount of offset can be modulated by an intersection point, andalso is influenced by offset coefficient data derivable from informationassociated with source geometry. These examples do not imply thatimplementations of these examples follow the same or similar processflow. For example, unless one computation requires an input from anothercomputation, computations can be selectively ordered. Also,implementations may be able to process or product certain information byconcurrent processing. As such, the linearized process flow shown in theexamples is for the sake of description and does not imply that animplementing algorithm would have to produce the values described insuch fashion. These examples show that one effect achieved in someimplementations is that secondary rays are traced from an origin that isoffset by an amount dependent on an intersection location on theprimitive; for example, where different primary rays intersect the sameprimitive at different locations and emit secondary rays, thesesecondary rays will have origins at different locations.

Further disclosure concerning example apparatus or components thereofwhich may implement the disclosed processes or portions thereof is foundwith respect to FIG. 10 and FIG. 11 below.

FIG. 10 depicts an example apparatus 300 in which aspects of thedisclosure can be practiced. Apparatus 300 comprises processor(s) 302that communicate with non-transitory memories, such as a cache hierarchy305, which can store a subset of data located in Random Access Memory(307). Non-volatile storage 309 may store data that is loaded into RAM307, including instructions for configuring processor(s) 302 to performprocesses implementing aspects of the disclosure. A User Interface (UI)311 may be provided to accept input from a user, although a UI is notnecessary in embodiments according to FIG. 10. A display 315 also may beprovided to display outputs of processing according to the disclosure.Outputs also may be stored in any one or more of the memories 305, 307and 309. Apparatus 300 may implement an intersection testing process,which performs by identifying a closest intersection of a ray having aspecified origin and direction with primitives defining objects locatedin a 3-D scene. This intersection testing function can be implemented bya process that accepts a definition for the ray and traverses the raythrough a scene acceleration structure comprising elements that boundsubsets of the primitives, and ultimately tests the defined ray forintersection any primitives not excluded from a potential intersectionby the traversal through the acceleration structure. A closestintersection identified, if any, can be used as an intersection pointaccording to the disclosure.

The definition of the secondary ray can be performed by a portion ofmachine executable code (e.g., a module of shader code) that is selectedin response to identifying an intersection between a primary ray and aprimitive. Ray tracing of a particular image can begin by emitting a setof primary rays that are traced from particular pixels of the 2-D image.Processes or portions thereof depicted in FIGS. 6-9 can be implementedby modules of shader code executing on processor(s) 302. An ApplicationProgramming Interface (API) can be used to provide a description of a3-D scene that is to be used in a ray tracing operation. The API can beimplemented by modules of machine executable code executing onprocessor(s) 302. The API can perform implementations of the processesdepicted in FIGS. 6-7, in order to pre-compute offset coefficients. TheAPI can determine an organization of data describing the 3-D scene, andthe pre-computed data, for use during ray tracing.

FIG. 11 depicts another example apparatus 320 that can be used toimplement a ray tracing according to the disclosure. Apparatus 320comprises a computation cluster 321 that has a plurality of computationcores, such as computation cores 330 and 331, each of which has aprivate L1 cache 325 and 326, and uses a shared L2 cache 340. Computecluster 321 sends data to a set of ray intersection test cells 350through a queue 342, and receives data from ray intersection test cells350 from queue 343. Ray intersection test cells 350 comprise computationthat is configured to execute one or more intersection testingalgorithms. For example, ray intersection test cells 350 may eachcomprise hardware logic that can be configured to perform anintersection test between a ray and an acceleration structure element orbetween a ray and a primitive. Separate dedicated fixed-functionhardware units can be provided for testing primitives or accelerationstructure elements for intersection. Ray intersection test cells 350also can be implemented as threads of computation executing on computecluster 321, or as a combination of threads of computation and separatehardware logic, fixed or configurable. Where ray intersection test cells350 are at least partially configurable, they can be configured fromconfigurable source 356. In one implementation, such configurationsource can be within a memory shared with compute cluster 321, or can bea dedicated configuration memory, such as a microcode or embeddednon-volatile storage co-located with the ray intersection test cells.

In an example, ray intersection test cells 350 may interface with a setof limited programmability circuits 352 that are configurable usingconfiguration information accessed from a configuration source 354.These limited programmability circuits 352 can be used for example, tocalculate dot products used in determining the offset coefficients orother related calculations. For example, these circuits can have aninput that accepts two vectors and performs a selected operation from apre-configured set of operations. In such an example, these coefficientsmay be returned with an intersection testing result, analogous toreturning barycentric coordinates for an intersection point. Rayintersection test cells 350 include one or more test cells.

The Appendix depicts a listing of machine readable instructions that canbe used to produce an implementation of the disclosure for applying thedisclosure to defining occlusion rays directed towards light sources.The instructions show an determining a measure of a size of a primitiveby determining difference of the form (an_dot_pos−(dot(artist_normal,p1))), where an_dot_pos is value of a DP between an artist vector(“artist normal”) for a specific vertex (e.g., p0), anddot(artist_normal, p1) represents a DP between that same artist normaland a vector directed from the scene origin to vertex p1. The depictedcode is for a triangular vertex and includes such calculation also forvertex p2. These calculations thus produce a value correlated to arelative size of the primitive. A reciprocal between the artist vectorfor a given vertex (e.g., p0) and the geometric normal for the primitivewill be a larger value when the artist vector is more divergent from thegeometric normal. Thus, this calculation makes larger offsetcoefficients for a particular vertex (e.g., p1off0, which is the offsetcoefficient for p1 in the direction to p0) when its artist vectordiverges more from the geometric normal for the primitive. The examplesrelated primarily to triangular primitives (whether individuallyspecified or specified as meshes or other kind of grouping). However,applications of the disclosure are not limited to triangles. Anotherexample of a primitive is a quadrilateral patch. Other primitives can bespecified with higher order functions, such as a spline functions. Ifusing non-triangular primitives, then an appropriate way to express ahit point on such primitive(s) can be provided. Thus, another embodimentwithin the disclosure is that data for a 3-D object includes data thatis encoded as per-vertex directional information, which can benormalized. Multiple of such per-vertex directional information, fromdifferent vertexes defining an intersected surface, is blended accordingto relative positions of those vertices with an intersection point onthe surface to produce an offset value. An example way in which thisblending can occur was provided above, along with an example of howcertain information used could be pre-calculated.

Although some subject matter may have been described in languagespecific to examples of structural features and/or method steps, it isto be understood that the subject matter defined in the appended claimsis not necessarily limited to these described features or acts. Forexample, a given structural feature may be subsumed within anotherstructural element, or such feature may be split among or distributed todistinct components. Similarly, an example portion of a process may beachieved as a by-product or concurrently with performance of another actor process, or may be performed as multiple separate acts in someimplementations. As such, implementations according to this disclosureare not limited to those that have a 1:1 correspondence to the examplesdepicted and/or described.

Above, various examples of computing hardware and/or softwareprogramming were explained, as well as examples how suchhardware/software can intercommunicate. These examples of hardware orhardware configured with software and such communications interfacesprovide means for accomplishing the functions attributed to each ofthem. For example, a means for performing implementations of each of theprocesses described herein includes machine executable code used toconfigure a machine to perform such process implementation. Other meansfor realizing implementations of the disclosed processes includes usingspecial purpose or limited-programmability hardware to realize portionsof the processes, while allocating overall control and management and adecision when to invoke such hardware to software executing on a generalpurpose computer. Combinations of software and hardware may be providedas a system to interface with software provided by third parties. Suchthird party software may be written to use a programming semanticspecified by the API, which may provide specified built-in functions orprovide a library of techniques that may be used during ray tracingbased rendering.

Aspects of functions, and methods described and/or claimed may beimplemented in a special purpose or general-purpose computer includingcomputer hardware, as discussed in greater detail below. Such hardware,firmware and software can also be embodied on a video card or otherexternal or internal computer system peripherals. Various functionalitycan be provided in customized FPGAs or ASICs or other configurableprocessors, while some functionality can be provided in a management orhost processor. Such processing functionality may be used in personalcomputers, desktop computers, laptop computers, message processors,hand-held devices, multi-processor systems, microprocessor-based orprogrammable consumer electronics, game consoles, network PCs,minicomputers, mainframe computers, mobile telephones, PDAs, tablets andthe like.

Aspects disclosed herein will generally exist in the context of largersystems and components of systems. For example, processing can bedistributed over networks, such as local or wide area networks and mayotherwise be implemented using peer to peer technologies and the like.Division of tasks can be determined based on a desired performance ofthe product or system, a desired price point, or some combinationthereof. In embodiments implementing any of the described units at leastpartially in software, computer-executable instructions representingunit functionality can be stored on computer-readable media, such as,for example, magnetic or optical disks, flash memory, USB devices, or innetworks of storage devices such as NAS or SAN equipment, and the like.Other pertinent information, such as data for processing can also bestored on such media.

In addition to hardware embodiments (e.g., within or coupled to aCentral Processing Unit (“CPU”), microprocessor, microcontroller,digital signal processor, processor core, System on Chip (“SOC”), or anyother programmable or electronic device), implementations may also beembodied in software (e.g., computer readable code, program code,instructions and/or data disposed in any form, such as source, object ormachine language) disposed, for example, in a computer usable (e.g.,readable) medium configured to store the software. Such software canenable, for example, the function, fabrication, modeling, simulation,description, and/or testing of the apparatus and methods describedherein. For example, this can be accomplished through the use of generalprogramming languages (e.g., C, C++), GDSII databases, hardwaredescription languages (HDL) including Verilog HDL, VHDL, SystemCRegister Transfer Level (RTL) and so on, or other available programs,databases, and/or circuit (i.e., schematic) capture tools. Embodimentscan be disposed in computer usable medium including non-transitorymemories such as memories using semiconductor, magnetic disk, opticaldisk, ferrous, resistive memory, and so on.

As specific examples, it is understood that implementations of disclosedapparatuses and methods may be implemented in a semiconductorintellectual property core, such as a microprocessor core, or a portionthereof, embodied in a Hardware Description Language (HDL)), that can beused to produce a specific integrated circuit implementation. A computerreadable medium may embody or store such description language data, andthus constitute an article of manufacture. A non-transitory machinereadable medium is an example of computer readable media. Examples ofother embodiments include computer readable media storing RegisterTransfer Language (RTL) description that may be adapted for use in aspecific architecture or microarchitecture implementation. Additionally,the apparatus and methods described herein may be embodied as acombination of hardware and software that configures or programshardware.

Also, in some cases terminology has been used herein because it isconsidered to more reasonably convey salient points to a person ofordinary skill, but such terminology should not be considered toimpliedly limit a range of implementations encompassed by disclosedexamples and other aspects. For example, a ray is sometimes referred toas having an origin and direction, and each of these separate items canbe viewed, for understanding aspects of the disclosure, as beingrepresented respectively as a point in 3-D space and a direction vectorin 3-D space. However, any of a variety of other ways to represent a raycan be provided, while remaining within the present disclosures. Forexample, a ray direction also can be represented in sphericalcoordinates. It also would be understood that data provided in oneformat can be transformed or mapped into another format, whilemaintaining the significance of the information of the data originallyrepresented.

Also, a number of examples have been illustrated and described in thepreceding disclosure, each illustrating different aspects that can beembodied systems, methods, and computer executable instructions storedon computer readable media according to the following claims. Bynecessity, not every example can illustrate every aspect, and theexamples do not illustrate exclusive compositions of such aspects.Instead, aspects illustrated and described with respect to one figure orexample can be used or combined with aspects illustrated and describedwith respect to other figures. As such, a person of ordinary skill wouldunderstand from these disclosures that the above disclosure is notlimiting as to constituency of embodiments according to the claims, andrather the scope of the claims define the breadth and scope of inventiveembodiments herein. The summary and abstract sections may set forth oneor more but not all exemplary embodiments and aspects of the inventionwithin the scope of the claims.

What is claimed is:
 1. A computer-implemented method of rendering animage of a 3-D scene using a ray tracing system, the method comprising:subsequent to an identification of an intersection between a first rayand a primitive located in the 3-D scene, emitting a secondary rayhaving an origin which lies on an implicit curved surface associatedwith the primitive, wherein said intersection between the first ray andthe primitive is at an intersection point, and wherein the origin of thesecondary ray is offset from the intersection point; and processing thesecondary ray for use in rendering the image of the 3-D scene.
 2. Themethod of claim 1, wherein the secondary ray is emitted in response tothe identification of the intersection between the first ray and theprimitive.
 3. The method of claim 1, wherein the origin of the secondaryray does not lie on the primitive.
 4. The method of claim 1, wherein thefirst ray is a primary ray, and wherein the primitive is a planarprimitive.
 5. The method of claim 1, wherein the origin of the secondaryray is offset from the intersection point by an offset amount whichvaries in dependence upon the position of the intersection point.
 6. Themethod of claim 1, wherein the origin of the secondary ray is offsetfrom the intersection point by an offset amount which is dependent on arelative position of the intersection point to vertices defining theprimitive in the 3-D scene.
 7. The method of claim 1, wherein the originof the secondary ray is offset from the intersection point by an offsetamount which is dependent on indicia of curvature calculated for theprimitive.
 8. The method of claim 7, wherein the indicia of curvaturecomprise coefficients associated with respective vertices of theprimitive and the offset is determined based at least in part on usingthe coefficients in a polynomial that weights the coefficients usingbarycentric coordinates of the intersection point.
 9. The method ofclaim 1, wherein offset coefficients are calculated for each vertexdefining the primitive, a value for each offset coefficient beingcalculated based on defining a respective perpendicular to a vectorassociated with each of the vertices defining the primitive, and whereinthe method further comprises mapping the intersection point to a pointon the implicit curved surface required to be tangent to each of theperpendiculars at the respective vertices.
 10. The method of claim 1,wherein the primitive is a triangle and a respective pair ofcoefficients are calculated for each of three vertices defining thetriangle, wherein the coefficients of a pair define an initial offsetfor the respective vertex towards each of the other two verticesdefining the triangle, and wherein these coefficients are modulated toproduce a final value for the origin offset, using barycentriccoordinates of the intersection point.
 11. The method of claim 1,wherein the planar primitive is a triangle and the origin offset isdetermined using barycentric coordinates for the intersection point todetermine a blending among offset coefficients associated with thevertices of the triangle, wherein each of the offset coefficients isdetermined based on a dot product of a vector associated with one of thevertices and a geometric normal associated with the primitive, weightedby a measure of a size of the primitive.
 12. The method of claim 1,wherein the offset of the origin from the intersection point is in adirection along a geometric normal of the primitive at the intersectionpoint.
 13. The method of claim 1, wherein the offset of the origin fromthe intersection point is along the incoming direction of the first ray.14. The method of claim 1, wherein said processing the secondary ray foruse in rendering the image of the 3-D scene comprises: tracing thesecondary ray through the scene to identify an intersection involvingthe secondary ray; and using the results of the tracing of the secondaryray in rendering the image of the 3-D scene.
 15. The method of claim 14,wherein the secondary ray is an occlusion ray, and the tracingdetermines whether a source of light in the direction of that occlusionray, if any, is prevented from reaching the surface of the primitive.16. A ray tracing system for rendering an image of a 3-D scene, the raytracing system comprising: a ray definition module configured to, basedon an identified intersection between a first ray and a primitivelocated in the 3-D scene, define a secondary ray to be emitted, thesecondary ray having an origin which lies on an implicit curved surfaceassociated with the primitive, wherein said intersection between thefirst ray and the primitive is at an intersection point, and wherein theorigin of the secondary ray is offset from the intersection point; andat least one processing unit configured to process the secondary ray foruse in rendering the image of the 3-D scene.
 17. The ray tracing systemof claim 16, wherein the origin of the secondary ray is offset from theintersection point by an offset amount which varies in dependence uponthe position of the intersection point.
 18. The ray tracing system ofclaim 16, wherein the offset of the origin of the secondary ray is alongone of the incoming direction of the first ray and a geometric normalfor the primitive at the intersection point.
 19. A non-transitorycomputer readable medium having stored thereon computer executableinstructions, which when executed cause at least one processor to renderan image of a 3-D scene by: in response to an identification of anintersection between a first ray and a primitive located in the 3-Dscene, emitting a secondary ray having an origin which lies on animplicit curved surface associated with the primitive, wherein saidintersection between the first ray and the primitive is at anintersection point, and wherein the origin of the secondary ray isoffset from the intersection point; and processing the secondary ray foruse in rendering the image of the 3-D scene.